1. Field of the Invention
The present invention relates to a flow rate control valve which can control the flow rate of a fluid. In particular, the present invention relates to a flow rate control valve of a proportional type using a solenoid.
2. Description of the Related Art
A flow rate control valve has been conventionally used to control the flow rate of a fluid flowing through a passage by changing the passage area in the valve if a pressure fluid is supplied to or discharged from an actuator.
According to a conventional flow rate control valve 1 shown in FIG. 3, a fluid passage 8 is generally opened and closed by manually operating a handle section 2 to enable a valve rod 4 to advance and retreat in an axial direction of the flow rate control valve 1. The handle section 2 is disposed upwardly of a body 3.
In the above case, a tapered tip end 9 of the valve rod 4 held by a seal 5 faces the fluid passage 8 defined between a fluid supply port 6 and a fluid discharge port 7. The flow rate of the fluid flowing from the fluid supply port 6 to the fluid discharge port 7 is controlled by the inserted degree of the tip end 9 into the fluid passage 8.
In the above conventional flow rate control valve 1, the manual operation enables the tip end 9 (valve plug) of the valve rod 4 to advance and retreat. However, the valve opening degree cannot be constantly controlled to a desired value since the above advancing and retreating movement is performed depending upon the operator""s manual operation.
Further, the operator""s manual operation cannot keep the fluid passage 8 and the valve plug airtight and liquid-tight with the valve plug being completely closed.
It is a general object of the present invention to provide a flow rate control valve which can set an arbitrary flow rate by electrically controlling the opening and closing operation of a valve plug and which can control the flow rate of a fluid highly accurately.